Download what is muscle memory?

by joe muscolino
body mechanics
The posture
of our body
is largely
determined by
the memorized
pattern of
baseline tone of
the musculature
of our body.
what is muscle memory?
The concept of muscle memory is vitally important in
the world of massage and bodywork. Yet, there seems to
be some controversy about what it is and how it works.
To better understand this idea and its application to clinical work, let’s explore the concept of muscle memory.
The Controversy
More controversial and more relevant to the world of
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Practiced Repeatedly
Simply put, muscle memory describes the idea that the
musculature of the body contracts in patterns, for both
posture and motion of the body. And these patterns are
memorized on some level, working without our conscious control. Hence, the term muscle memory.
There is little controversy surrounding the idea of
memorized patterns of muscle contraction for movement.
By practicing certain activities such as walking, swinging
a tennis racquet, playing a piece of music on the piano,
or driving a car while drinking a cappuccino and adjust-
ing the radio dial, we learn to execute these complex and
coordinated activities with little or no input from the part
of the brain that controls voluntary, willed muscle contractions—the cerebral primary motor cortex.
Instead, once a movement pattern has been initially
learned in the cerebral motor cortex, it is transferred to
the basal ganglia, located deeper within the brain. Consequently, it’s possible for people to execute complex
coordinated movement patterns while paying little or
no attention, perhaps even thinking of something else
entirely. Thinking in these terms, the concept of muscle
memory as it relates to movement seems fairly straightforward: memorized movement patterns are stored in
and released from the basal ganglia of the brain.
body mechanics
Illustrations From Muscolino JE: Kinesiology: The skeletal System
and Muscle Function, Enhanced Edition. St. Louis, 2006, Mosby. Modified by Jeannie Robertson.
Regular
muscle fibers
Muscle spindle
fibers
Figure 1. Muscle spindle fibers are a specialized type of
muscle cell. They are located within a muscle and lie parallel to the regular muscle fibers.
Spinal cord
Sensory
neuron
LMNs
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Synergist
muscle
Muscle spindle
Muscle
Reflex
hammer
Figure 2. Cross section of the spinal cord and the muscle
spindle stretch reflex. The muscle spindle reflex is triggered to occur when the muscle is either stretched too
far or stretched too quickly, as when stretched too quickly
by being hit with a reflex hammer as shown. This reflex
causes lower motor neurons (LMNs) to direct the muscle
and its synergists to contract.
massage and bodywork, however, is how the concept of
muscle memory relates to posture. The posture of our
body is largely determined by the memorized pattern
of baseline tone of the musculature of our body. By exerting pull upon the bones and joints, resting baseline
muscle tone determines the position, or posture, of our
body. Indeed, when clients visit a massage therapist,
the usual complaint is that their resting baseline tone
of musculature is too tight. Musculoskeletally, the most
common goal of massage therapy is to change the muscle memory of baseline resting tone of the tight muscles
of our clients.
So, let’s explore the idea of muscle memory in this
context. The first misconception is the belief that postural muscle memory resides in muscle tissue itself. The
muscular system is an amazingly complex and awe-inspiring system of the body, but it does not hold the key
to its own memory. Certainly, adhesions present within
musculature and its fascia can determine its ability to
stretch, affecting its degree of passive tension and, in
turn, the body’s posture. But when we refer to actual
muscle tone—or muscle contraction—the memory resides somewhere else.*
This idea can be easily understood by considering a
person who has suffered a traumatic injury that severs
the lower motor neurons (LMNs) that synapse with and
control a muscle. In these cases, the muscle will become
flaccidly paralyzed and have no ability to contract, unless electrical stimulation is applied from the outside. If
the memory for the muscle contraction were actually
within the muscle, however, it would be able to contract
regardless of nerve function.
The Grand Master
If not in the muscle itself, where does muscle memory
for baseline resting tone reside? Similar to the muscle
memory for movement patterns, muscle memory for
baseline resting tone resides in the nervous system, the
grand master of all muscular function. However, this
muscle memory isn’t stored in the basal ganglia, but in
a different region of the brain known as the gamma motor system.
The gamma motor system controls resting muscle
tone via muscle spindle fibers. Muscle spindle fibers are
specialized muscle cells that are sensitive to stretch.
They are located within the belly of the muscle, lying
parallel to the regular muscle fibers (Figure 1). When
*This rule is not true of myofascial trigger points (TrPs). The tone of the fibers of a TrP is due to local phenomena. For more on this, please see the
“Body Mechanics” column in the Spring 2008 issue of mtj.
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body mechanics
the muscle is either stretched too long or too quickly,
the muscle spindle fibers are stimulated and send an impulse within sensory neurons into the spinal cord. These
sensory neurons synapse with LMNs and cause them to
send a signal for contraction to the regular muscle fibers
of the muscle and its synergists (Figure 2).
When the muscle contracts toward its center, it is
no longer stretched, preventing it from being overly
stretched and torn. For this reason, the muscle spindle
reflex, also known as the stretch reflex, is viewed as a
protective reflex.
The critical aspect of this mechanism is that the sensitivity of the muscle spindle fibers can be set by specialized LMNs known as gamma LMNs. These in turn are
controlled by gamma upper motor neurons (UMNs) that
are located within the brain and operate subconsciously
(Figure 3). When this gamma motor system of the brain
orders the muscle spindle fibers to contract and shorten, they become less tolerant of being stretched and
therefore more apt to trigger the muscle spindle stretch
reflex. The stretch reflex will then cause the muscle to
contract and tighten to match the tone of the spindle
fibers within. On the other hand, if the gamma motor
system does not contract the muscle spindle fibers they
will be longer and more tolerant to being stretched—and
less likely to trigger the stretch reflex.
As we move our bodies with normal daily activities,
we inevitably stretch our muscles to some degree because when we order a muscle on one side of a joint
to contract and shorten to cause movement, its antagonists on the other side of the joint must lengthen and
stretch to allow this movement to occur. If and when
this stretch exceeds the tolerance of the muscle spindle
fibers, they will trigger the stretch reflex. Hence, resting muscle tone comes to mirror the tone of the muscle
spindle fibers. In this manner, spindle tone determines
the muscle memory of resting baseline muscle tone in
our body.
Thus, when we are working on a client’s tight muscle,
what we are really trying to accomplish is to lower the
gamma motor system activity so that the muscle spindle
fibers will relax, allowing the regular fibers of the muscle
to relax. We may be working directly on the muscle, but
we do so to affect its gamma spindle activity in regions of
the brain that act subconsciously. In effect, we are trying to alter the patterns of spindle tone that have already
been set.
Gamma UMN
Regular
muscle fibers
Muscle
spindle
Muscle
Spinal cord
Gamma LMN
Figure 3. Cross section of the spinal cord and muscle
spindle fibers within a muscle. The sensitivity of muscle
spindle fibers to stretch is determined by gamma lower
motor neurons (LMNs) that direct the muscle spindle fibers to contract and shorten. These gamma LMNs are
controlled by gamma upper motor neurons (UMNs) that
originate in the brain.
Whether this pattern has been in place for months,
years or even decades is critically important. As a general rule it is the chronicity, not severity, of a tight muscle
that is the primary factor that determines how long it
takes to loosen it. Put simply, when it comes to changing
muscle memory for tight muscles, the purpose of massage, as well as stretching, is to alter gamma motor activity of the brain so that we can change muscle spindle
tone, and thereby change resting muscle tone.
n
Joseph E. Muscolino, DC, is an
instructor at the Connecticut Center
for Massage Therapy and the owner of
The Art and Science of Kinesiology in
Redding, Connecticut. He is also the
author of The Muscular System Manual
and Kinesiology, The Skeletal System
and Muscle Function textbooks (Elsevier, 2005 and
2006). Visit Joseph’s website at www.learnmuscles.
com.